Orchestrator logging interface + Docker implementation

[guzman-raphael]

This issue relates to adding compute logs in:

• PodRunAPI trait (see below)
• local docker orchestrator implementation
• PodResult (see below)

// orchestrator/mod.rs
pub trait PodRunAPI: Types {
    // ...
    fn get_logs(&self) -> Result<String>;
    // ...
}

// model.rs
pub struct PodResult {
    // ...
    pub logs: String,
    // ...
}

Depends on #18, #12